English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Conformational energies of n-butane, n-pentane, and n-hexane have beencalculated at the CCSD(T) level and at or near the basis set limit.Post-CCSD(T) contribution were considered and found to be unimportant. The datathus obtained were used to assess the performance of a variety of densityfunctional methods. Double-hybrid functionals like B2GP-PLYP and B2K-PLYP,especially with a small Grimme-type empirical dispersion correction, arecapable of rendering conformational energies of CCSD(T) quality. These werethen used as a `secondary standard' for a larger sample of alkanes, includingisopentane and the branched hexanes as well as key isomers of heptane andoctane. Popular DFT functionals like B3LYP, B3PW91, BLYP, PBE, and PBE0 tend tooverestimate conformer energies without dispersion correction, while the M06family severely underestimates GG interaction energies. Grimme-type dispersioncorrections for these overcorrect and lead to qualitatively wrong conformerorderings. All of these functionals also exhibit deficiencies in the conformergeometries, particularly the backbone torsion angles. The PW6B95 and, to alesser extent, BMK functionals are relatively free of these deficiencies.  Performance of these methods is further investigated to derive conformerensemble corrections to the enthalpy function, $H_{298}-H_0$, and the Gibbsenergy function, ${\rm gef}(T)\equiv - [G(T)-H_0]/T$, of these alkanes. While$H_{298}-H_0$ is only moderately sensitive to the level of theory, ${\rmgef}(T)$ exhibits more pronounced sensitivity. Once again, double hybridsacquit themselves very well.

Performance of ab initio and density functional methods for conformational equilibria of CnH2n+2 alkane isomers (n=2-8)